A hybrid motor vehicle comprises at least one electric motor and at least one heat engine. This motor and engine can drive the same driving wheels or different driving wheels. In a hybrid operating mode the electric motor and heat engine simultaneously transmit a mechanical torque to at least one driving wheel, whether a positive engine torque or a resistive negative torque.
The invention relates to the category of these hybrid vehicles able to operate also in a purely combustion mode, in which only the heat engine transmits a mechanical torque to the driving wheels. Among the motor vehicles targeted by the invention, there is a category referred to as bi-mode, these vehicles also being capable of operating in a purely electric driving mode, in which the heat engine does not transmit any mechanical torque to the driving wheels.
To this end, it is known that the powertrain may comprise a connection device making it possible to selectively couple or decouple the electric motor and heat engine to/from the driving wheels. In other words, the connection device makes it possible to couple or decouple the heat engine to/from at least one driving wheel and makes it possible to couple or decouple the electric motor to/from at least one driving wheel, which may or may not be the same driving wheels. In the purely combustion/electric mode, only the heat engine/electric motor contributes to the traction, whereas in the hybrid mode the electric motor and heat engine can contribute to the traction. Reference is also made to clutching and declutching when a motor element is coupled to the wheel.
However, the invention also relates to motor vehicles that cannot operate in such a purely electric mode and that are able to operate only in the purely combustion mode and in the hybrid mode. In this case, the connection device makes it possible solely to couple or decouple the electric motor.
In the prior art it is also known, in the case of an electric motor working as an engine to drive the vehicle in purely electric driving mode or in hybrid driving mode, to operate this electric motor in accordance with a braking principle referred to as regenerative braking, i.e. with energy recovery. From an electrical viewpoint, the electric motor then works as a generator and converts the mechanical energy applied to its rotor into an electrical current, which can then be regulated in an electric motor controller as a current for charging a battery, for example intended to power the electric motor. In this regenerative braking mode the consumption of mechanical energy produced by the electrical conversion applies a braking torque to the wheels of the vehicle. On the one hand, the vehicle as a result can be at least partially braked with the aid of the electric motor operating as a generator, and on the other hand the kinetic energy recovered by the braking can be stored in electrochemical form in an accumulator or battery, this energy being reusable thereafter in order to propel the vehicle or for ancillary functions.
It is known that this regenerative braking can be controlled during braking phases per se, i.e. when the driver presses on the brake pedal of the vehicle. The invention does not relate to this field of control.
However, regenerative braking has been developed preferably so as to be controlled and implemented during phases of deceleration without braking, i.e. when the driver releases the pressure on the accelerator pedal without actuating the brake pedal, said pedal tending to lift. The invention relates to this field of control of mechanical torque. It is known to provide for the fact that the stroke of the acceleration pedal is divided at a neutral point, for which the torque transmitted to the wheels by the powertrain is zero, into a first braking-adjustment stroke and a second acceleration-adjustment stroke. Above the neutral point, the powertrain transmits an engine torque to the driving wheels. Below the neutral point, the powertrain transmits a resistive torque to the driving wheels.
This resistive torque can be wholly (apart from output) converted into electrical energy in the case of a purely electric operating mode. In the case of the hybrid operating mode, this resistive torque can be divided into a torque produced by the engine brake of the heat engine and into a regenerative braking torque by the electric motor, which converts the kinetic energy of its rotor into electricity.
Document FR-A1-2749229 in the name of the applicant states that the regenerative braking torque at the electric motor is dependent on the speed at which a foot is removed from the accelerator pedal.
Document FR-A1-2945243, also in the name of the applicant, states that the amplitude of the braking-adjustment stroke by the accelerator pedal is dependent on the charge of the battery.
These known solutions are satisfactory in the case of hybrid motor vehicles not subject to a coupling and to a decoupling of the electric motor and heat engine. However, these documents do not take into consideration a possibility of this type of clutching and declutching, and these solutions cannot be used in such cases.
In effect, this would result in problems with regard to the perceived comfort because, when a foot is removed from the accelerator pedal by the driver, the vehicle would brake too suddenly in the event of clutching: during phases of clutching and declutching, the transition from regenerative operation to non-regenerative operation and vice versa is disruptive for passengers due to a feeling of hard braking.
On the other hand, in the specific case envisaged by the invention of a bi-mode vehicle (capable of operating not only in hybrid mode but also in purely electric mode), the feeling perceived by passengers during phases of deceleration is not identical in the purely electric mode and in the hybrid mode, in particular during changes between modes as the vehicle is travelling.